First and second pharyngeal arch syndromes are congenital defects caused by a failure of neural crest cells to migrate into the first pharyngeal arch which can produce facial anomalies. Examples of first arch syndromes include Treacher Collins syndrome and Pierre Robin syndrome.
In the first two months of pregnancy, tissues from each side of a fetal head and neck grow toward one another and fuse at the centerline. These tissues are known as the pharyngeal arches or visceral arches; they form the crucial bones, skin, nerves, muscle, and other features of the head and neck. These pairs of tissue are composed of six separate arches.
The first arches produce the lower jaw, two bones in the middle ear, and nerves and muscles for chewing. The second arches give rise to the nerves and muscles of facial expression, one bone in the middle ear, most of the outer ear, and parts of the bone above the larynx (voice box). The third arches produce the nerves for swallowing and the rest of the bone above the larynx. The remaining arches give rise to the nerves for the vocal cords and other nerves and cartilage in the neck.
Anything that disrupts this process — whether in the production, growth, or movement of key cells in the arches — will cause parts of the face to develop abnormally. The problem may occur in both sides of the face, in which case it is considered a ‘symmetrical’ condition, or predominantly on one side, when it is considered asymmetrical, or uneven. Children with these disorders often have ear abnormalities and mandibular hypoplasia, an underdeveloped lower jaw.
What are asymmetrical pharyngeal arch syndromes, and what do they look like?
Microtia and atresia. Children with microtia and atresia do not hear well and have ears that look abnormal .In children with microtia, the outer, visible portion of the ear (the pinna or auricle) is underdeveloped. The result can be an ear that looks otherwise normal, but is too small. There can be a miniature ear that is folded and joined to the side of the head, with bits of skin attached where the ears would normally be, or skin tags on the cheek. In atresia, by contrast, the ear canal, which carries sounds from the outside to the inner ear, is either closed off or absent. Microtia and atresia usually occur together. Typically they are part of hemifacial syndrome.
Hemifacial microsomia (HFM). This is the second most common type of facial anomaly, after cleft lip and cleft palate. Hemifacial microsomia is known by a variety of other names, including craniofacial microsomia, first and second pharyngeal arch syndrome, Goldenhar syndrome, and lateral facial dysplasia. It occurs when soft tissue and bone from the pharyngeal arches on one side of a child’s face fails to develop fully. The result is that facial and jaw bones in the area are smaller than normal. Although it generally occurs on just one side of the face, it can also appear on both sides.Children with HFM have several common facial features. They may have one-sided (unilateral) or two-sided (bilateral) underdevelopment of the eye, cheekbone, lower jaw, facial nerve and muscles. Bits of skin and cartilage may occur in front of the ears. There may be hearing loss from underdevelopment of the middle ear. The soft palate (the fold of tissue at the back of the mouth that separates the mouth from the nasal cavity) may move to the unaffected side because of muscle weakness on the affected side. The tongue may be small with nerve weakness on the affected side. In about 40 percent of children with HFM, the nerve responsible for moving the facial muscles is weak on the affected side or, rarely, on both sides. About a third of children with the disorder have macrostomia, literally ‘large mouth,’ because of an opening at the corner of the mouth. Typically, microtia and atresia are part of hemifacial syndrome.
How common are these conditions?
Hemifacial microsomia occurs in about one in 5,600 births. On average, one in 10,000 babies is born with microtia and/or atresia. Among the Navajo people, however, the condition is considerably more common, arising in about one in 1,200 births.
Why was my child born with a pharyngeal arch anomaly?
The cause of these conditions is not known. They usually occur at random — that is, in families without a history of the condition — but in rare families, they are passed on from generation to generation. A geneticist or genetic counselor can help you assess the possibilities.
If my child has microtia or atresia, is there a risk for other problems as well?
In some children with these conditions, a nerve known as the seventh, or facial, nerve may be located in an unusual position. Because the nerve is responsible for movements of the face, its small size or underdevelopment may prevent children from registering the full range of emotions on their faces. The more affected the external ear, the more likely the facial nerve will function improperly.
Will microtia and atresia affect my child’s hearing ability?
Most likely, yes. Most children with these conditions have moderate hearing loss and can’t distinguish sounds below 40 to 60 decibels. (People with normal hearing, by contrast, can hear sounds of 15 decibels or less.)
Ear anomalies tend to be associated with abnormalities of the kidneys; both develop at the same time. A renal (kidney) ultrasonic scan is indicated whenever there are abnormal ears.
Can such hearing problems be alleviated?
Yes. By using a bone conduction hearing aid, children with microtia and/or atresia can hear well enough to participate in conversations. Such hearing aids send sound waves directly to the tiny bones in the inner ear that are used for hearing, bypassing the eardrum and ear canal.
If my child has hemifacial microsomia, is there a risk for other problems?
Some children with hemifacial microsomia develop a cyst below the skin (called dermoid), often near the seams of the head bones, such as the eyebrow or around the nose. Five to 10 percent of children have such cysts on the cornea of the eye or in the soft tissue around the eye. About 15 percent of children with hemifacial microsomia have a cleft lip or palate. There is also the possibility of anomalies beyond the head; this is called the HFM “;expanded spectrum.” Your care team will evaluate your child’s heart, bones, kidneys, and extremities.
What nervous system disorders are associated with hemifacial microsomia?
Disorders of the central nervous system occur in five to 15 percent of children with hemifacial microsomia. Among them is Dandy-Walker malformation, a condition characterized by a cyst in a portion of the brain known as the cerebellum, which is involved in coordinating the muscles and maintaining equilibrium. The cyst may interfere with the body’s ability to drain fluid from the brain and spine, resulting in hydrocephalus, or enlargement of the head.
Does hemifacial microsomia worsen with time?
No. If a child starts life with relatively minor differences, these will not change.
Can the problems associated with hemifacial microsomia be corrected?
Often, yes. But because the condition varies so greatly from child to child, it is important that you work closely with your child’s multidisciplinary craniofacial team to develop a treatment plan for your child’s unique needs. The bone and soft tissue problems associated with the condition can be corrected or improved with operations, and physical therapy can help your child exercise muscles that may be underdeveloped and weak.
What other conditions are similar to, but distinct from, hemifacial microsomia?
There are three similar inherited conditions that are autosomal dominant disorders (50/50 chance of being passed on).
Townes-Brocks syndrome. An extremely rare condition (only 200 cases have been identified worldwide), in which children have two or more of the following problems: malformations of the anus, hand deformities, external ear abnormalities, and nerve-related deafness. These malformations can range from minor to severe, and individuals may not have all of them.
Branchio-oto-renal (BOR) syndrome. This genetic disorder includes malformations of the ear and cysts and sinus tracts in and near the neck, hearing loss, and malformations of the kidney. There are varying combinations of these problems, in differing degrees. Malformations on the ears can include cupping of the outer ear, very small holes in front of or on the outer ear, tags of skin in front of the ear, and cysts on the neck. Kidneys can be smaller than usual or have a malformation that does not interfere with function or cause any symptoms. If the malformations are severe, however, they may predispose the child to kidney disease. Most people with BOR syndrome do not experience any type of kidney problem.
Branchio-oto-facial (BOF) syndrome. This is a very rare birth defect that is characterized by low birth weight; an abnormal pit, opening, or skin abnormality behind both ears; distinctive malformations of the head and facial area; abnormalities of the eyes; and premature graying of the scalp hair in adolescence. Some people with the syndrome may have a cleft palate or cleft lip. Other problems can include a broad, misshapen nose and malformed ears. Eye problems may include unusually small size, clouding of the lenses, crossing, wide spacing, and an absence of tissue from the colored portion of the eye.
What are the types of symmetrical pharyngeal arch syndromes, and what do they look like?
There are two major categories: Treacher Collins syndrome and Nager syndrome.
Treacher Collins (“mandibulafacial dysostosis, or MFD”) syndrome. Unlike the asymmetrical conditions described above, children with Treacher Collins syndrome have underdeveloped structures on each side of the face, usually to the same degree. And, unlike some children with asymmetrical conditions, children with Treacher Collins syndrome do not have weakness of the facial muscles.The features of Treacher Collins syndrome include some or all of the following: downward-slanting eyelids; notching (colobomas) of the lower eyelids; underdevelopment of the bones of the face, including the cheekbones (zygomas), lower jaw (mandible), and upper jaw (maxilla); an abnormal bite (malocclusion); a smaller than average face; underdeveloped and/or malformed ears; hearing loss, which is often severe, due to a narrowing or absence of the ear canal.A very rare condition that is similar to Treacher Collins syndrome is known as Miller or Wildervanck-Smith syndrome. Its characteristics include underdeveloped cheekbones, an abnormally small jaw, a cleft palate, small, protruding “cup-shaped” ears, and drooping of the lower eyelids. In addition, some children with the syndrome have incomplete development of one or more of the limbs, webbing of the fingers or toes, absence of the little fingers or toes, and underdevelopment of bones in the forearm. The condition does not, however, affect a child’s intelligence.
Nager syndrome. Children with this condition share many of the problems of those with Treacher Collins syndrome. It is distinguished by flat cheeks, down-slanting eyes, almost total absence of eyelashes, low-set, cup-shaped ears, and a very small lower jaw. Children with the condition also have underdeveloped thumbs and forearms and may have genitourinary abnormalities or heart problems.
What health problems are associated with Treacher Collins and Nager syndromes?
Some children have difficulty breathing as a result of the underdeveloped lower jaw, which doesn’t leave sufficient space in the mouth for the tongue. This problem may lessen as children grow larger, but during infancy a tube may be inserted in the throat (a procedure known as a tracheostomy) to ensure they take in enough oxygen. Underdevelopment of the jaw can also produce eating or swallowing problems. And hearing loss occurs in most children with these conditions.
Why does my child have this condition?
Scientists have discovered the genetic mutation (error) that is responsible for Treacher Collins syndrome. In most children with the condition, neither parent carries the mutation — it occurs early in fetal development, possibly at conception. If a father or mother carries the genetic mutation for Treacher Collins syndrome, however, there is a 50:50 chance with each pregnancy of having an affected child.
How common is Treacher Collins syndrome?
It is estimated that about one in 10,000 children is born with the syndrome. The actual rate may be somewhat higher, because some cases are so minor that they are not diagnosed.
What treatments are available for my child?
nfants with eating and swallowing problems can often be helped by a feeding tube, special nipple, and special infant formula. Children with hearing loss may need a hearing aid and speech and language therapy to improve their communication abilities. If your child has a breathing problem, a monitor can alert you if he or she experiences breathing difficulties while asleep. Surgical procedures are available to improve facial appearance. Your child’s multidisciplinary craniofacial team will advise you on what to expect from these operations and when they should be performed. Because the condition is more severe in some children than in others, the need for and type of reconstructive surgery varies from child to child.
How can I ensure my child receives the best treatment?
It’s essential that your child’s care is planned by a multidisciplinary craniofacial team that includes specialists in a variety of medical, dental, and other health care areas.
Do these conditions affect my child’s intelligence?
Children with Treacher Collins syndrome have the same range of intelligence as any other children.
- Hemifacial Microsomia – “Information for Parents”
Booklet by John B. Mulliken, M.D. on: Hemifacial Microsomia
Children’s Hospital Boston, Craniofacial Centre, 300 Longwood Avenue, Boston, MA 02115
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- Treacher Collins Foundation